Voltage regulator employing a nonlinear impedance and negative temperature coefficient impedance to prevent leakage current



3,21 1,989 D NEGATIVE E CURRENT 1965 M. MINTZ ET AL VOLTAGE REGULATOREMPLOYING A NON-LINEAR IMPEDANCE AN TEMPERATURE COEFFICIENT IMPEDANCE ToPREVENT LEAKAG Original Filed May 19, 1958 2 Sheets-Sheet 1 INVENTORS.

Oct. 12, 1965 M. MINTZ ET AL 3,211,989 VOLTAGE REGULATOR EMPLOYING ANON-LINEAR IMPEDANCE AND NEGATIVE TEMPERATURE COEFFICIENT IMPEDANCE TOPREVENT LEAKAGE CURRENT Original Filed May 19, 1958 2 Sheets-Sheet 2 1mQ ZJQQ 4 N 46a r- [550. 4 E3 w REGULATED I SOQ P 54 2Q D C 54a. VOLTAGE[N i L UNREGULATED 62a D C VOLTAC: E.

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MART/N Ml/vrz Bs/e'ro/v JAMES M co/ue INVENTORS.

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United States Patent VOLTAGE REGULATOR EMPLOYHNG A NON- LINEAR IMPEDANCEAND NEGATIVE TEM- PERATURE COEFFICIENT IMPEDANCE T0 PRE- VENT LEAKAGECURRENT Martin Mintz, Woodland Hills, and Berton J. McCornb, Torrance,Calif., assignors, by mesne assignments, to TRW Inc., a corporation ofOhio Continuation of application Ser. No. 736,ti47, May, 19, 1958. Thisapplication Dec. 7, 1961, Ser. No. 161,327

6 Claims. (Cl. 323-22) This invention relates to power supply circuitsand, while not limited thereto, is herein described with reference to atransistorized voltage regulator circuit embodying the invention. Thepresent application is a continuation of our copending applicationSerial No. 736,047, filed May 19, 1958, entitled Power Supply nowabandoned.

While transistorized voltage regulator circuits are known that providesubstantially constant direct current output voltage, such circuits havenot proven entirely satisfactory due to certain inherent characteristicsof transistors. For example, a load short circuit often results in thedestruction of some of the transistors in the regulator circuit. The useof fuses in such regulator circuits has not proven practical due to thecomparatively long lag time of fuses conventionally available-thetransistors in such circuits usually burn out before the fuses areactuated. Then, too, such transistorized circuits have not operatedreliably under conditions of extreme temperature changes, such as wouldbe encountered in power supplies in airborne applications. For example,high ambient temperatures often result in excessive leakage currentthrough the transistors (especially at low or zero signal current)leading to poor regulation and low power output, and sometimes to thedestruction of the transistors. Furthermore, previous voltage regulatorcircuits have not been completely satisfactory in providing desirablevoltage regulation over different output or load voltages.

Accordingly, one of the objects of this invention is the provision of animproved transistorized circuit capable of operation at relatively highambient temperatures and at the same time capable of sustaining loadshort circuits without harm.

Another object is the provision of an improved fuseless protectivearrangement for a transistorized power supply circuit.

A further object of the invention is the provision of an improvedtransistorized voltage regulator circuit capable of maintainingdesirable operating characteristics over relatively wide temperaturevariations.

Still another object is the provision of an improved voltage regulatorcircuit capable of providing substantially uniform load voltageregulation substantially independent of the magnitude of the loadvoltage.

In accordance with one of the features of the invention, atransistorized circuit is provided that is self-protective against loadshort circuits or overloads. When subjected to such an overload, thecircuit ceases operation until reset. The circuit of the inventionincludes two transistorized stages. The first of the stages, a loadcurrent regulator stage, is controlled by the second or bias controlamplifier stage. The bias control amplifier stage, connected to controlthe flow of bias current to the first stage during normal operation ofthe circuit, is connected to be biased into conduction by the flow ofload current through the first or load current control stage. Once inoperation, the circuit will pass load current until a reduction in loadvoltage, caused by a load short circuit or overload, causes a reductionin conduction bias to the second stage; this bias reduction cuts otf theoperation of the entire circuit. According to the invention, a startingor auxiliary biasing lead is provided; this biasing lead is adapted tobe either manually or automatically temporarily connected to the secondor bias control stage for initiating load current flow. Thus, thetransistorized circuit of the invention is constructed so that once itis biased into operation it remains in stable operation providingself-biasing until a load short circuit or overload is encountered,whereupon the output of the circuit ceases until the starting biasreferred to is again applied.

According to another feature of the invention a transistorized circuitincludes a reverse biasing network to compensate for transistor leakagecurrent at high ambient temperatures. This compensation is realized byproviding, at high temperatures, a path from a current source directlyto the transistor base (by-passing the transistor emitter), with thispath having a lower impedance than the path from the current sourcedirectly to the transistor emitter. The transistor base (with a p-n-ptype transistor) is thus biased at a positive potential higher than thatof the emitter (in the absence of signal current flow). As a consequenceof this reverse biasing, no appreciable leakage current flows throughthe emitter at high ambient temperatures (leakage current flow throughthe emitter would be amplified and, at high temperatures, may be largerthan the signal current). The reverse biasing network of the invention,as embodied in the circuit referred to, makes use of a non-linearvoltage dropping element, such as a unilateral conduction device thathas a substantially constant voltage drop across it regardless ofcurrent fiow through it (for example, a crystal diode). This non-linearvoltage dropping element is connected in series with an emitter lead ofthe transistor of the first or load current amplifier stage, and anegative temperature coefficient resistance device (such as athermistor) is connected to by-pass current flow directly to the baselead of the transistor. If leakage current flows through the transistor,a voltage drop occurs across the non-linear element (the voltage dropbeing usually a fraction of a volt in the case of a crystal diode).Since a smaller voltage drop takes place across the negative temperaturecoeflicient resistance device than across this non-linear voltagedropping element, the flow of leakage current causes the base to becomemore positive than the emitter at high temperatures by virtue of thevoltage drop across the non-linear element. This reverse bias conditiontends to reduce leakage current through the transistor by biasing thetransistor base toward cut-off.

Yet another feature of the invention is the provision of an improvedoutput or load voltage control for a transistorized voltage regulatorcircuit such as the one described above. A variable, positive feedbackarrangement is connected to adjust load voltage regulation in theregulator circuit independently of the magnitude of the output voltageto be regulated. This arrangement is realized by means of a variableresistor connected in series with the reference voltage source of thevoltage regulator, and between the regulator circuit input and output.Adjustment of this variable resistor varies the bias voltage (from a tapon a voltage sensing network) to the load current control stage of theregulator without any appreciable effect on the load voltage. Thus,desirable voltage regulation may be realized over a range of differentload voltages.

In the drawings, wherein like reference characters refer to like circuitelements and features:

FIGURE 1 is a circuit diagram of a two-stage transistorized voltageregulator circuit embodying the inven tion; and

FIG. 2 is a diagram of a three-stage transistorized voltage regulatorcircuit embodying the invention.

Referring now to FIG. 1, direct current is fed into input terminals 12and 14 of a series type transistorized voltage regulator circuit 16embodying the invention from a conventional direct current power supplysource 10, and is taken from the regulator circuit by means of outputterrninals 17 and 18. The regulator circuit 16 illustrated by way ofexample includes: (a) a two-stage amplifier to provide the amplificationrequired for voltage regulation, the amplifier being made up of twoseries-connected transistors 20 and 22 of opposite polarity types; (b) abreakdown or zener diode 24 for establishing a reference potential forthe circuit; an output voltage sensing network including twoseries-connected resistors 26 and 28; and (d) an output filter hereillustrated as capacitors 32 and 56, the second capacitor 56 serving toincrease the high frequency gain of the voltage regulating feedback loopby lowering the alternating current impedance of the loop.

In accordance with the invention, the regulator circuit 16 alsoincludes, as will be explained in detail below: (a) a novel amplifierbiasing circuit, comprising a resistor 34 and a switch 36 connected inseries, for turning on the voltage regulator circuit after it has beenautomatically turned off as a result of being subjected to an outputshort circuit as well as for initiating the operation of the regulatorcircuit; (b) a novel reverse biasing circuit, comprising a non-linearvoltage dropping device such as a crystal diode 38 and a negativetemperature coefficient resistance device such as a thermistor 40, forpermitting operation of the amplifier transistors 20 and 22 at highambient temperatures without excessive leakage current; and (c) a novelpositive feedback circuit including the variable resistor 42, forimproved output voltage regulation.

In the two-stage amplifier of the voltage regulator circuit the firsttransistor 20 carries the full load current i while the secondtransistor 22 acts as a bias control or feedback amplifier thatregulates the load current flow through the first transistor. The firstor load current regulator transistor 20 is therefore preferably a highpower transistor, while the second or bias control transistor 22 may bea low power one. In operation of the voltage regulator circuit 16 aconstant output voltage E which may, for example, be 25 volts, isprovided from a varying input voltage E, which may, for example, benominally 30 volts. The excess input voltage E E volts in the example)is taken up substantially across the collector 46 to base 48 junction ofthe first transistor 20. Any tendency toward increasing output voltagecauses a compensating increase in voltage between the collector 46 andemitter 44 of the first transistor due to the reduction in the flow offirst transistor biasing current i through the collector 50 of thesecond transistor 22.

In detail, in the regulator circuit 16 load current i from the positivevoltage source terminal 12 flows into the first transistor 20 (a p-n-ptype) through the emitter 44 thereof, and out of the transistor throughthe collector 46 (assuming an appropriate bias on the transistor base48). The load current i then flows toward the positive output terminal17. The negative return through the voltage regulator circuit is fromthe negative output terminal 18, through the positive feedback resistor42 to be described, and to the negative input terminal 14. The biasingcurrent i of the first transistor 20 flows into the emitter 44 thereofand out through the base 48. This biasing current i then becomes theload current through the second transistor 22 (an n-p-n type). Thiscurrent i flows through a current limiting resistor 55, connectedbetween the first transistor base 48 and the second transistor collector50, through the second transistor collector 5t and out of the emitter52. The flow of bias current i for the second transistor 22 is, duringnormal operation of the voltage regulator circuit, into the transistor22 through the base 54 thereof and out of the transistor through theemitter 52 thereof, and finally to the negative voltage source terminal14.

The current supply i for the voltage reference or zener diode 24 flowsfrom the positive side of the output circuit through a voltage droppingresistor 30 to the diode 24, then through the positive feedback resistor42 to the negative source terminal 14. The combined biasing current 1'and zener diode supply current i is referred to in the drawing as i Inoperation of the regulator circuit 16 of FIG. 1, the starting switch 36is closed (as by being manually closed or by being automatically closedby, for example, an automatic switch connected to close the circuit fora short period of time when initiation of current flow is desired). Thisclosing of the starting swtich initiates the flow of a starting orauxiliary biasing current to the second transistor 22 causing it tobecome conductive. When the second transistor 22 becomes conductive,biasing current z' for the first transistor 20 is applied to the firsttransistor causing it to become conductive. The first and secondtransistors 20 and 22 are thus turned fully on until the output voltageE builds up to a value where the error voltage between the outputsensing circuit and voltage reference circuit is essentially zero (thesensing circuit being the series resistors 26 and 28, and the referencecircuit being the zener diode 24 and resistor 42). Any potentialdifference or error voltage between a sensing circuit pickoff point(point A) and the reference potential (the potential at the base 54 ofthe second transistor 22) affects the bias on this second transistor 22;the error voltage is thus amplified and phase inverted by this secondtransistor 22, so as to appear as a potential across the emitter 44 tocollector 46 junction of the first transistor 20, cancelling the errorvoltage. At this point of operation, the voltage regulator circuit isstable and he output is regulated. The switch 36 is then opened and theregulation continues since both transistors 20 and 22 are conductive.Since the circuit reaches stable operation in a very short period oftime, the switch may in practice be only momentarily closed in order toinitiate operation. Once regulation of the output voltage is realized,the zener diode supply rsistor 30 supplies substantially all of thezener diode current and the second transistor biasing current. Thecurrent for the zener diode is taken from the output side of the voltageregulator circuit 16 so that minimum current changes are imposed on thevoltage reference circuit. Capacitors 32 and 56 may be connected in aconventional manner to stabilize and improve the transient performanceof the regulator circuit.

In the event of an output short circuit, the reference voltage, acrossthe zener diode 24, will drop to zero. This drop causes the base 54 ofthe second transistor 22 to have the same potential as that of theemitter 52 thereof. Since, as is known, the base must be more positivelybiased than the emitter for an n-p-n transistor to remain conductive,the second transistor 22 now ceases to conduct. When the secondtransistor is cut off, no first transistor 20 biasing current i canflow; this cuts off the operation of the first transistor 20. Theforegoing sequence results in a cessation in the operation of thevoltage regulator circuit. Thus the circuit is inherently selfprotectiveagainst output short cirucits. Since the base 54 of the secondtransistor must be made more positive than the emitter in order toinitiate operation of the circuit, the circuit remains ofi even afterthe removal of the output short circuit. In order to reestablishoperation of the circuit, the switch 36 is again momentarily actuated,allowing the reference voltage to build up, rendering the secondtransistor 22 conductive, and thus starting the flow of output currentfrom the regulator circuit.

While the transistors have been described with reference to a firsttransistor 20 of a p-n-p type and a second transistor 22 of an n-p-ntype, it will be appreciated that the polarity types of the transistorsmay be reversed, with the polarity of other circuit connectionssimilarly reversed so as to effect the circuit operation described.Also, while the switch 36 has been indicated as being a momentarily onswitch, it will be appreciated that other switching arrangements may beused for starting the flow of output voltage. For example, a magneticrelay or thermal switch may be used to establish a bias on the secondtransistor 22 for starting the operation of the regulator circuit.

According to another feature of the invention, an improved reversebiasing circuit is provided that permits operation of transistors athigh ambient temperatures without excessive leakage current. While thisfeature is of especial utility in the use of germanium transistors, italso proves useful with other types of transistors, such as those of thesilicon variety. The reverse biasing circuit is made up of a non-linearvoltage dropping element that has a substantially constant voltage dropcharacteristic thereacross, that is, a substantially constant voltagedrop across it regardless of current flow through it, and a negativetemperature coefiicient device. The non-linear voltage dropping deviceis here exemplified by the crystal diode 38, and the negativetemperature coefiicien-t device by the thermistor 40. The thermistor 40has a voltage drop characteristic thereacross that is substantiallygreater than that of the crystal diode 38 at normal temperatures, thatis, at temperatures at which the transistor 20 exhibits substantially noleakage current flow. However, at temperatures substantially higher thannormal, where the transistor exhibits leakage current flow, thethermistor 40 exhibits a voltage drop characteristic thereacross that isat least as small as that across the crystal diode 38. The diode 38 isconnected in'series with the first transistor emitter 44 for conductionin a direction toward the transistor 20, and the thermistor 40 isconnected between the positive side of the source voltage and thetransistor base 48. At low ambient temperatures the thermistor 40 actssubstantially as an open circuit allowing transistor operation in themanner described above. In the event of high ambient temperatures, thethermistor 40 lowers the external resistance between the emitter 44 andthe base 48 to a value less than the resistance across the diode 38.This lowered external resistance allows leakage current (in the absenceof signal current) to flow directly to the transistor base 48, biasingthe base to a value more positive than the emitter. This reverse biasingtends to cut off the transistor to the flow of leakage current. The flowof leakage current through the transistor is undesirable since thiscurrent flow would be amplified by the transistor and may, at hightemperatures, be larger than the signal current flow.

According to still another feature of the invention, a variable resistor42 is used as a positive feedback control element for adjusting the loadvoltage regulation substantially independently of the magnitude of theoutput voltage provided by the regulator circuit. The feedback controlaccording to this feature is used to let the voltage sensing portions ofthe regulator circuit see (in the presence of an output voltage drop dueto increased load current) a voltage change greater than that whichactually takes place across the output terminals 17 and 18. Theresultant over compensation for load circuit voltage drop is used toprovide improved voltage regulation.

Normally, the voltage of the power delivered by a power supply decreaseswith increasing load. A voltage regulator circuit usually serves tominimize the voltage drop (rather than compensate for the voltage drop).According to this feature of the invention, the sensitivity of thevoltage regulator circuit is increased so as to maintain the outputvoltage substantially uniform regardless of load. Indeed, the circuitaccording to this feature can actually be adjusted to provide increasingvoltage with increased load! The load voltage is sampled at point A, thepotential at point A varying in proportion to the instaneous value ofthe actual load voltage. In order to increase the sensitivity of thecircuit to changes in load, point A is connected to appear to drop inpotential at a faster rate than the rate at which the load voltageactually tends to decrease with increasing load. This simulation of theeffect of a great drop in output voltage is used to let the voltageregulator circuit compensate to a greater degree than it would in theabsence of this simulated great voltage drop. Thus the regulator is madeto see a greater change than that which actually exists in the output.The actual amount of over compensation is chosen (by adjustment of theresistance of the variable resistor 42) such that, over the variationsin load over which the regulator circuit is designed to operate, theoutput voltage remains substantially uniform at the desired level. Theforegoing is realized by having the reference source, zener diode 24, inseries with the feedback control resistor 42. Adjustment of the variableresistor 42 determines the potential of point B, the connection betweenthe zener diode 24 and the variable resistor 42, for adjusting the levelof the voltage applied to the zener diode 24. The variable resistor 42is connected in series between the negative input and output terminals14 and 18, respectively, and in series with the reference potentialsource, the zener diode 24. The voltage magnitude control resistor 28 isof the order of thousands of ohms resistance, while the feedback controlresistor 42 is of the order of a fraction of an ohm to a few ohms inresistance. From the foregoing it is seen that the variable outputvoltage control resistor 28 adjusts the magnitude of the output voltageE while the variable feedback control resistor 42 is used to adjust therate of voltage compensation of the circuit to changes in load current.

FIG. 2 is a circuit diagram of a three-stage voltage regulator circuitembodying the principles described with respect to FIG. 1. The circuitportions in the diagram of FIG. 2 corresponding to circuit portions inthe diagram of FIG. 1 will be referred to with the same numerals asthose used in FIG. 1 with the exception that the letter a will be usedto designate the circuit portions of FIG. 2.

The three-stage transistorized voltage regulator circuit 16a of FIG. 2is similar both in circuit arrangement and in operation to that of FIG.1 with the exception that an intermediate amplifier stage is connectedin cascade between the first and second amplifier stages illustrated inthe circuit of FIG. 1. This intermediate amplifier stage, provided by atransistor 70a of the same polarity type as that in the first regulatorstage 20a, contributes to the provision of an over-all circuit havinggreater gain, and thus improved voltage regulation action, than that ofthe circuit of FIG. 1. The second transistor 70a is connected so thatthe biasing current of the first transistor 20a flows through the secondtransistor 70a under the control of this second transistor. The biascurrent for the second transistor 70a, in turn, flows through, and iscontrolled by, the last transistor 22a. Thus, each transistor controlsthe flow of bias current in the transistor in the stage preceding it.While a single inter-mediate stage is used in the circuit of FIG. 2, itwill be appreciated that any number of intermediate amplifier stages maybe used between the input and output amplifiers (provided by transistors20a and 22a, respectively) for providing increased gain and resultantincreased voltage regulation control. The additional intermediateamplifier stages are serially connected in the regulator circuit in amanner similar to that of the intermediate stage of the regulatorcircuit of FIG. 2.

As is the case with the first transistor 29a, a high temperature,reverse biasing, leakage current compensation arrangement is providedfor the second transistor 70a. This compensation arrangement is made upof a crystal diode 58a and thermistor 60a connected to the base 48a ofthe first transistor 20a and to, respectively, the emitter 72a and base76a of the second transistor 70a. The function and connection of theseelements 58a and 60a are substantially the same as those in thepreceding stage where the diode 38a and thermistor 40a provide leakagecurrent compensation for the first transistor 20a at high ambienttemperatures. As is the case in the circuit of FIG. 1, a currentlimiting resistor 55a is connected between the collector 50a of thefinal transistor 22a and the base 76a of the transistor 70a of thepreceding stage for limiting the current flow and dissipation of thelast transistor 22a. Also, a number of diodes may be connected in seriesso that the total voltage drop across the diodes provides the desiredreference voltage. Thus, for example, two serially connected zenerdiodes 62a and 64a .are used in the circuit of FIG. 2.

While the invention has been described as embodied in an improvedtransistorized voltage regulator circuit for a power supply, it isapparent that the principles may be applied to other transistoriz/edcircuits where circuit immunity from load short circuits and/ orincreased temperature and voltage operation versatility is desired.

What is claimed is:

1. In combination:

a direct current source,

load means,

a semiconductor device having a principal current path including inputand output electrodes and a control current path including said inputelectrode and a control electrode,

means for connecting said principal current path and said load means inseries across said source,

means responsive to variation-s in the output voltage applied to saidload means and connected to said control electrode for regulating theimpedance of said principal current path as a function of said outputvoltage,

a non-linear impedance device connected in series with said principalcurrent path between said input electrode and said source, and

a negative temperature coefficient resistance means connected in shuntwith the series combination of said control current path and saidnon-linear impedance device.

2. In a voltage regulation circuit:

.a source of unregulated voltage direct current;

a load circuit;

a semiconductor device having a principal current path includingcollector and emitter electrodes and a control current path includingsaid emitter electrode and a control electrode;

means for connecting said principal current path and said load circuitin series across said source;

means for sensing variations in the voltage applied to said loadcircuit;

means responsive to said sensing means for applying a control current tosaid control current path as a function of the voltage applied to saidload circuit so that the impedance of said principal current path isvaried as a function of the load circuit voltage;

a non-linear impedance voltage dropping means connected in series withsaid principal current path between said emitter and said source fordeveloping a relatively constant biasing potential in response to apredetermined range of load currents flowing therethrough; and

negative temperature coefficient resistance means connected across theseries combination of said control current path and said voltagedropping means for shunting a greater portion of said control current 8around said semiconductor device in response to increased ambienttemperatures and vice versa.

3. A control circuit suitable for use in regulating the supply of powerto an output load from a source of electrical power, said circuitcomprising:

first and second transistors each having a base and current input andoutput portions, said second transistor being coupled in such a biasingrelationship to said first transistor as to conduct all bias currentflow of said first transistor so that only during conduction of saidsecond transistor is said first transistor conductive;

a leakage current compensation network including a non-linear impedancevoltage dropping element having one end connected to the current inputportion of said first transistor, and a negative temperature coefficientresistance device connected between the other end of said non-linearimpedance voltage dropping element and the base of said firsttransistor;

voltage-sensitive means connected at one end to the base of said secondtransistor to prevent current fiow therethrough when the voltage dropacross the output load is less than a predetermined value; and

a voltage-divider arrangement connected across the output load and tothe other end of said voltage-sensitive means, a voltage tap on saidvoltage-divider arrangement being connected to the current outputportion of said second transistor;

said second transistor remaining conductive as long as the voltageacross the load is greater than said predetermined value as a functionof the voltage drop across said voltage-sensitive means.

4. The circuit defined in claim 3 wherein said nonlinear impedancevoltage dropping element is a diode connected for normal conduction in adirection of normal current flow through said first transistor, saidnegative temperature coeflicient resistance device is a thermistor, andsaid voltage-sensitive means is a zener diode.

5. The circuit defined in claim 4 wherein said circuit further includesauxiliary by-pass biasing means momentarily connectable to the base ofsaid second transistor for initiating conduction of said secondtransistor to initiate current flow through said first transistor whenthe voltage across the output load is conditionally less than saidpredetermined value.

6. A control circuit suitable for use in regulating the supply of powerto an output load from a source of electrical power, said circuitcomprising:

first and second transistors each having a base and current input andoutput portions, said second transistor being coupled in such a biasingrelationship to said first transistor as to conduct all bias currentflow of said first transistor so that only during conduction of saidsecond transistor is said first transistor conductive;

means coupled to the base of said second transistor for establishing abi-level reference potential thereat, the potential being substantiallyat one level during normal conductive operation of the control circuitand at the other level upon overload of the output load;

an output voltage sensing network coupled to the output load for sensingan overload condition, said network additionally being coupled to theoutput current portion of said second transistor and to said means;

a biasing circuit for selectively rendering said second transistorconductively operative after it has been rendered inoperative inresponse to an overload condition; and

a reverse-biasing circuit including a non-linear impedance voltagedropping device and a negative temperature coefiicient resistance devicerespectively coupled in series between the input current portion of saidfirst transistor and the base thereof for permitting 9 operation of saidfirst transistor without excessive 2,871,376 leakage current. 2,885,4942,892,165 References Cited by the Examiner 3,026,469 UNITED STATESPATENTS 5 3,105,198

2,866,017 12/58 Jones 323-22 10 Kretzmer 323-68 X Darlington et a1330-23 Lindsay 32322 Wilbur et a1 323--22 Higginbotham 330-23 LLOYDMCCOLLUM, Primary Examiner.

2. IN A VOLTAGE REGULATION CIRCUIT; A SOURCE OF UNREGULATED VOLTAGEDIRECT CURRENT; A LOAD CIRCUIT; A SEMICONDUCTOR DEVICE HAVING APRINCIPAL CURRENT PATH INCLUDING COLLECTOR AND EMITTER ELECTRODES AND ACONTROL CURRENT PATH INCLUDING SAID EMITTER ELECTRODE AND A CONTROLELECTRODE; MEANS FOR CONNECTING SAID PRINCIPAL CURRENT PATH AND SAIDLOAD CIRCUIT IN SERIES ACROSS SAID SOURCE; MEANS FOR SENSING VARIATIONSIN THE VOLTAGE APPLIED TO SAID LOAD CIRCUIT; MEANS RESPONSIVE TO SAIDSENSING MEANS FOR APPLYING A CONTROL CURRENT TO SAID CONTROL CURRENTPATH AS A FUNCTION OF THE VOLTAGE APPLIED TO SAID LOAD CIRCUIT SO THATTHE IMPEDANCE OF SAID PRINCIPAL CURRENT PATH IS VARIED AS A FUNCTION OFTHE LOAD CIRCUIT VOLTAGE; A NON-LINEAR IMPEDANCE VOLTAGE DROPPING MEANSCONNECTED IN SERIES WITH SAID PRINCIPAL CURRENT PATH BETWEEN SAIDEMITTER AND SAID SOURCE FOR DEVELOPING A RELATIVELY CONSTANT BIASINGPOTENTIAL IN RESPONSE TO A PREDETERMINED RANGE OF LOAD CURRENTS FLOWINGTHERETHROUGH; AND NEGATIVE TEMPERATURE COEFFICICENT RESISTANCE MEANSCONNECTED ACROSS THE SERIES COMBINATION OF SAID CONTROL CURRENT PATH ANDSAID VOLTAGE DROPPING MEANS FOR SHUNTING A GREATER PORTION OF SAIDCONTROL CURRENT AROUND SAID SEMICONDUCTOR DEVICE IN RESPONSE TOINCREASED AMBIENT TEMPERATURE AND VICE VERSA.